Ovrednotenje silicijevih mikropasovnih detektorjev kot rentgenskih senzorjev za digitalno mamografijo

Background. Position sensitive silicon microstrip detectors are used as sensors for X rays in a digital imaging system. Silicon detectors were used inan edgeon geometry, yielding high X ray detection efficiency. Material and methods. A small detector system was assembled and tested. Images of a standard, 5 cm thick phantom were made and evaluated. It is demonstrated, thatthe use of silicon detectors in mammography could significantly contributeto a reduction of dose. All images were made with skin entrance doses lower than 1 mGy. Results and conclusion. Microcalcifications with a diameter of 350microm could still be detected with skin entrance doses of about 0.25 mGy. It was demonstrated that a 5 Ip/mm pattern can be detected. Image processing should further improve the image quality.Izhodišče. Pozicijsko občutljive silicijeve detektorje smo uporabili kot senzorje rentgenskih žarkov v sistemu za digitalno rentgensko slikanje. Silicijevi detektorje smo uporabili v t. i. geometriji "na rob", kjer rentgenski žarki zadenjejo detektor s strani, zato lahko dosežemo visok izkoristek detekcije - preko 80% pri energiji rentgenskih fotonov 20 keV. Material in metode. Sestavili in testirali smo majhen sistem. Posneli smo slike standardnega, 5 cm debelega fantoma in jih ovrednotili. Rezultati in zaključki. Silicijevi detektorji lahko znatno prispevajo k zmanjšanju doze primamografskih preiskavah. Vse slike so bile posnete pri vstopni kožni dozi do 1 mGy. Mikrokalcifikacije s premerom 350 microm so še vedno vidne z vstopnokožno dozo 0.25 mGy. Pokazali smo, da z našim sistemom uspešno zaznamo testni vzorec črt z gostoto 5 parov na mm. Z nadaljno digitalno obdelavo lahkoše dodatno izboljšamo kvaliteto slik

Neutron irradiation test of depleted CMOS pixel detector prototypes

Charge collection properties of depleted CMOS pixel detector prototypes produced on p-type substrate of 2 k$\Omega$cm initial resistivity (by LFoundry 150 nm process) were studied using Edge-TCT method before and after neutron irradiation. The test structures were produced for investigation of CMOS technology in tracking detectors for experiments at HL-LHC upgrade. Measurements were made with passive detector structures in which current pulses induced on charge collecting electrodes could be directly observed. Thickness of depleted layer was estimated and studied as function of neutron irradiation fluence. An increase of depletion thickness was observed after first two irradiation steps to 1$\cdot$10$^{13}$ n/cm$^{2}$ and 5$\cdot$10$^{13}$ n/cm$^{2}$ and attributed to initial acceptor removal. At higher fluences the depletion thickness at given voltage decreases with increasing fluence because of radiation induced defects contributing to the effective space charge concentration. The behaviour is consistent with that of high resistivity silicon used for standard particle detectors. The measured thickness of the depleted layer after irradiation with 1$\cdot$10$^{15}$ n/cm$^{2}$ is more than 50 $\mu$m at 100 V bias. This is sufficient to guarantee satisfactory signal/noise performance on outer layers of pixel trackers in HL-LHC experiments

Behaviour of beryllium-7 and lead-210 time series measured in Serbia and Slovenia over 1991-2015

6th International Conference on Radiation and Applications in Various Fields of Research (RAD), Book of Abstracts, Jun 18-22, 2018, Ohrid, Macedoni

New evidence of dominant processing effects in standard and oxygenated silicon diodes after neutron irradiation

Abstract Silicon diodes processed on standard and oxygenated silicon substrates by three different manufacturers have been irradiated by neutrons in a nuclear reactor. The leakage current density ( J D ) increase is linear with the neutron fluence. J D and its annealing curve at 80°C do not present any sizeable dependence on substrate oxygenation and/or manufacturing process. The acceptor introduction rate ( β ) of the effective substrate doping concentration ( N eff ) is independent from the oxygen concentration when standard and oxygenated devices from the same manufacturer are considered. On the contrary, β significantly varies from one manufacturer to another showing that the β dependence on the particular process can be important, overtaking the small substrate oxygenation effect. Finally, the average saturation value of the N eff reverse annealing is slightly lower for the oxygenated samples, pointing out a positive effect of the substrate oxygenation even for devices irradiated by neutrons

Factor analysis of the beryllium-7 and lead-210 specific activities in surface air, and meteorological parameters

Međusobna povezanost specifičnih aktivnosti berilijuma-7 i olova-210 u prizemnom sloju atmosfere sa meteorološkim parametrima razmotrena je u faktorskoj analizi. Merenja su sprovedena u Beogradu, Republika Srbija, i u Ljubljani i Krškom, u Republici Sloveniji, tokom 1991–2015 godine. Na sve tri lokacije, faktorska opterećenja dva faktora pokazuju da je: 1) specifična aktivnost berilijuma-7 obuhvaćena faktorom 1 sa temperaturom, oblačnošću i relativnom vlažnošću; dok je 2) specifična aktivnost olova-210 obuhvaćena faktorom 2 sa količinom padavina i atmosferskim pritiskom. Iako je komunalitet već dva faktora veći od 0,5 za većinu posmatranih varijabli, tek uvođenjem trećeg faktora komunalitet za specifičnu aktivnost olova-210 i atmosferskog pritiska na sve tri merne lokacije raste na preko 0,5. Rezultati faktorske analize pokazuju da se specifične aktivnosti berilijuma-7 i olova-210 u prizmenom sloju atmosfere nalaze pod različitim dominantnim uticajima. Koncentracija berilijuma-7 je pod uticajem faktora regionalnog karaktera, koji je takođe dominantan za srednju temperaturu. Ova veza specifične aktivnosti berilijuma-7 i temperature preko dominantnog zajedničkog faktora važi i kada se broj faktora u analizi poveća na tri i četiri. Sa druge strane, na koncentraciju olova-210, kao i na količinu padavina i atmosferski pritisak, više uticaja ima lokalni faktor. Ova povezanost olova-210 sa druga dva meteorološka parametra, međutim, prestaje da važi sa povećanjem broja faktora u analizi na tri, kada se izdvaja specifičan faktor koji objašnjava preko 80% varijanse specifične aktivnosti olova-210.An association between the beryllium-7 and lead-210 specific activities in surface air and meteorological parameters is investigated using factor analysis. The measurements were conducted in Belgrade, Republic of Serbia, and Ljubljana and Krško, Republic of Slovenia, over 1991–2015. In all the locations, the factor loadings of two factors show that: 1) the beryllium-7 specific activity is encompassed by factor 1 together with temperature, cloud cover and relative humidity; while 2) the lead-210 specific activity, precipitation and atmospheric pressure are described by factor 2. Although the communalities of only two factors are already larger than 0.5 for most of the variables, an introduction of a third factor raises the communalities of all the variables above 0.5. The results imply that the beryllium-7 and lead-210 are under different dominant underlying mechanisms. The concentration of beryllium-7 seems to be primarily influenced by a mechanism of a regional character which is also a predominant factor for temperature. This association between the beryllium-7 specific activity and temperature prevails even when the number of factors in the analysis is raised to three and four. The lead-210 specific activity, on the other hand, together with precipitation and atmospheric pressure, is under an influence of a local mechanism, but that relationship between the variables ceases to hold when the number of factors is raised to three, and more than 80% of the variance in the Pb-210 specific activity is explained by one specific factor.Article is part of: [http://vinar.vin.bg.ac.rs/handle/123456789/8245

Timing Performances and Radiation Hardness of 3D Diamond Detectors

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Beryllium-7 activity concentration trends in Serbia and Slovenia

Beryllium-7 is a natural radionuclide used as a tracer of the stratospheric-tropospheric exchange. Its abundance in the surface air is expected to change as the temperatures in the atmosphere increase. To investigate the temporal trends of the beryllium-7 activity concentrations and temperature, we apply spectral analysis to time series from three sampling sites: Belgrade in Serbia, and Ljubljana and Krško in Slovenia. The sites lie close to the 45 ºN parallel, with Krško approximately 400 km and Ljubljana around 500 km west of Belgrade. Between January 1991 and December 2019, the air filter samples were collected using air samplers; a monthly composite sample was formed and analysed by gamma spectrometry. We use monthly mean temperature records from the European Climate Assessment & Dataset, the Republic Hydrometeorological Service of Serbia for Belgrade, and the Slovenian Environment Agency for the sites in Slovenia. In the spectral analysis decomposition, we look into a term called trend that represents the overall growth (increase or decrease) in the data records. The trend is calculated using a linear fit. All three sites show 1) positive temperature trends, however statistically insignificant (at the 95 % confidence level), and 2) statistically significant beryllium-7 activity concentration trends of 2.26 %/year, 1.13 %/year, and 0.50 %/year in Belgrade, Ljubljana, and Krško, respectively. The results confirm our initial hypothesis–over the 28 investigated years, the beryllium-7 activity concentrations increase in the surface air. On the other hand, the non-significant temperature rise in our records suggests that within our method, the temporal resolution of one month is insufficient for obtaining a statistically significant temperature trend

Development of 3D detectors at FBK-irst

We report on the development of 3D detectors at Fondazione Bruno Kessler - irst in the framework of the CERN RD-50 Collaboration. Technological and design aspects dealing with the 3D Single Type Column detectors are reviewed, and selected results from the electrical and functional characterization of prototypes are reported and discussed. A new detector concept, namely 3D Double-side Double Type Column detectors, allowing for significant performance enhancement while maintaining a reasonable process complexity, is final ly addressed

The ABC130 barrel module prototyping programme for the ATLAS strip tracker

For the Phase-II Upgrade of the ATLAS Detector, its Inner Detector, consisting of silicon pixel, silicon strip and transition radiation sub-detectors, will be replaced with an all new 100 % silicon tracker, composed of a pixel tracker at inner radii and a strip tracker at outer radii. The future ATLAS strip tracker will include 11,000 silicon sensor modules in the central region (barrel) and 7,000 modules in the forward region (end-caps), which are foreseen to be constructed over a period of 3.5 years. The construction of each module consists of a series of assembly and quality control steps, which were engineered to be identical for all production sites. In order to develop the tooling and procedures for assembly and testing of these modules, two series of major prototyping programs were conducted: an early program using readout chips designed using a 250 nm fabrication process (ABCN-25) and a subsequent program using a follow-up chip set made using 130 nm processing (ABC130 and HCC130 chips). This second generation of readout chips was used for an extensive prototyping program that produced around 100 barrel-type modules and contributed significantly to the development of the final module layout. This paper gives an overview of the components used in ABC130 barrel modules, their assembly procedure and findings resulting from their tests.Comment: 82 pages, 66 figure

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements